The watch would not have left the factory that way, with one fixed and one spring bar. Now I don't know which style is original, (but that specific spring bar size does not look original to the watch, as shown in the picture).
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The solid bar would require you push a pin through a hole in the lugs to release the bar.
OK I see the problem on Bonhams site, you had two mis-matched straps right? The previous owner cobbled something up to sell and left you to sort it out :-( Measure the lug width and get yourself a pair of stainless steel spring bars to fit, likely 17mm. Rather than scratch your lugs trying to dig out that fixed bar, just cut it in the middle with snips. Did it come with a VC buckle